TITLE: GCN CIRCULAR NUMBER: 40485 SUBJECT: Konus-Wind detection of GRB 250516A DATE: 25/05/18 13:53:49 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report The long GRB 250516A (Fermi GBM detection: Fermi GBM team, GCN 40466; Mukherjee & Meegan, GCN 40473; Swift detection: Beardmore et al., GCN 40467) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~11 sigma count-rate increase in the interval from T0-2.757 s to T0+23.739 s where T0 = 14:35:29 UT. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250516A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.21 (-0.10, + 0.10) and Ep = 164(-9,+10) keV. Modelling the spectrum near the peak count rate (T0+3.131 s to T0+9.019 s) by a CPL function yields alpha = -1.35 (-0.10, + 0.11) and Ep = 403(-53,+82) keV. In the 20 keV -10 MeV band, standard for the KW analysis, the burst fluence is (4.41 ± 1.33)x10^-6 erg/cm^2 and the 2.944 s peak energy flux, measured from T0+6.075 s, is (5.85 ± 0.42)x10^-7 erg/cm^2/s. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...